The present invention relates to a magnetically driven centrifugal pump, particularly of a single suction structure, in which an impeller is rotated by way of a magnetic coupling between a magnets-embedded follower rotor interconnected with the impeller and a magnets-embedded drive rotor interconnected with an electric motor.
In the conventional centrifugal pump of a single suction structure of the above-mentioned type, the impeller is fixed to the outward end portion of the rotating shaft which is rotatably supported in the center line of a pump casing by way of a supporting member attached internally to the casing. Furthermore, a radial bearing of ceramic material resistant to hard wear is interposed between the rotating shaft and the supporting member so as to withstand a high speed of rotation of the rotating shaft.
In the operation of the above-described centrifugal pump, the magnets-embedded drive rotor is rotated directly by an electric motor, and the magnets-embedded follower rotor opposed inside to the drive rotor is rotated accordingly by indirect way of a magnetic coupling, so that the rotating shaft and the impeller are caused to rotate integrally with the follower rotor. With the rotation of the rotating shaft and the impeller, the impeller imparts centrifugal force to the liquid coming into a suction port which is configured in the axial center of the impeller, thus carrying the liquid radially in an accelerated manner.
However, when the impeller pressurizes and discharges the liquid, the impeller adversely receives an uneven reaction of axial load (i.e., thrust) and radial load, and hence the rotating shaft especially at high speedy rotation is subjected to unbalanced vibration. Accordingly, the ceramic radial bearing and a ceramic thrust bearing, which can withstand hard wear but is relatively low in toughness against breakage, i.e. in brittleness, are likely to suffer damage or breakage due to the influence of axial load and impact occurring with the vibration of the rotating shaft at high speedy rotation.
To solve the above-described problem of the prior art, the inventor of the present application has previously proposed an improvement in the magnetically driven centrifugal pump, as disclosed in U.S. Pat. No. 5,160,246, where a cushioning member is mounted on the impeller rotating shaft in the position between a rotational side thrust bearing of ceramic put adjacent to a non-rotational side ceramic radial bearing and a flange provided integrally on the middle of the rotating shaft so as to positively push the thrust bearing continuously outwards from the rear against the radial bearing, directly. In this arrangement, the vibration of the rotating shaft at high speedy rotation is absorbed and lessened by the cushioning member.
According to the above-described arrangement of the improved pump, the cushioning member is arranged to rotate integrally with the impeller rotating shaft and the rotational side ceramic thrust bearing, so that the cushioning member's absorption of vibration of the rotating shaft at a high speedy rotation is limited relatively to a certain degree. Furthermore, since the ceramic thrust bearing displaces in an axial or radial direction or a vectorial direction at a high speedy rotation of the rotating shaft, a chattering phenomenon takes place to the cushioning member, and further spreads multiply to the rotational side thrust bearing and the non-rotational radial bearing to thereby result in the damage or breakage of their bearings, especially of the thrust bearing.
It is accordingly a primary object of the present invention to provide a magnetically driven centrifugal pump, in which there is no fear of damage and breakage of the ceramic bearings, so designed as to relieve the influence of thrust load and vibration of the impeller rotating shaft at high speedy rotation upon the ceramic bearing by absorbing such thrust load and vibration.
It is a secondary object of the present invention to provide a magnetically driven centrifugal pump so designed as to give a preferable cushioning effect to the ceramic bearings without a likelihood that a chattering phenomenon occurs in a cushioning member arranged for absurbing the vibration of the impeller rotating shaft at a high speedy rotation.
It is a further object of the present invention to provide a magnetically driven centrifugal pump so designed as to prevent the likely vibration of the rotation shaft at high speedy rotation by the operation of a so-called self-aligning.
It is a further object of the present invention to provide a magnetically driven centrifugal pump so designed as to save the likely wear and fatigue on the ceramic radial bearing due to contact with the rotation shaft by cooling the frictional heat which generates between the radial bearing and the rotating shaft.
With the above and other objects in view, the present invention provide a magnetically driven centrifugal pump so designed that a drive power of an electric motor is transmitted from a magnets-embedded drive rotor to a magnets-embedded follower rotor opposed to one another for formation of a magnetic coupling; comprising a pump casing separated internally by a partition into two rooms of which one accommodates the drive rotor and the other accommodates the follower rotor, a rotating shaft holding the follower rotor on an inward portion thereof while holding an impeller on an outward end portion, the rotating shaft being supported with a radial bearing of ceramic material of non-rotation which is fitted into a supporting member fixed in the pump casing, a thrust bearing of ceramic material being secured to the rotating shaft for integral rotation and juxtaposed in a condition of contact with said radial bearing of non-rotation so as to receive an axial load of the rotating shaft, and a cushioning member being mounted compressedly in an interspace between a front end of the thrust bearing and a circular edged projection of the supporting member which are opposed to one another.
Preferably, the radial bearing has an exterior surface curved outwards like the bilge of a barrel, while an interior surface of the radial bearing is provided with a spiral groove.